The regulation of natural killer (NK) cells has been widely studied because of the numerous important protective and regulatory functions NK cells are thought to fulfill in vivo. The long range goal of this project is the thorough understanding of how NK activity is regulate at the cellular and molecular levels. Specifically, the present proposal seeks to test three hypotheses which are derived from previous data. (1) The first hypothesis suggests that monocytes augment NK activity of enriched null cell populations through an ILI-IL2 pathway. It proposes that monocytes augment the NK activity by supplying either membrane-associated ILI or another surface component pius soluble ILI to the enriched null cells. This results in (a) increased IL2 receptor (IL2R) affinity and/or increased numbers of IL2R/ cell and/or increased numbers of cells with IL2R; and (b) increased IL2 production by NK cells. The final proposed step is the IL2-induced activation of a population of non LGL target-binding cells in the enriched null cell population (2) The second hypothesis is that IL2R participate in the IL2 radiated augmentation of human NK activity. (3) The third hypothesis is that the monocyte mediated augmentation of NK activity enables NK cells to lyse fresh tumor target cells, which are normally insensitive to NK cells. A corollary is that the monocyte mediated modulation of NK is altered in cancer patients. The specific aims and methods to test these hypotheses are: (i) To demonstrate the presence of membrane IL1 on human monocytes and correlate it with the monocyte mediated augmentation. (ii) To assess changes in IL2R numbers and affinity in enriched null cells and NK cell lines following exposure to monocytes. (iii) To test at the molecular level for changes in IL2 production by the cell types in the enriched null cell population following exposure to monocytes. (iv) To characterize the cell which is susceptible to the monocyte effect. (v) To assess IL2R changes and IL2-mRNA production in resting and IL2-stimulated null cells and LGL. (vi) To assess the vulnerability of normally insensitive fresh tumor cells to monocyte-augmented NK activity. And (vii) to determine the correlation between the augmentative capacity of monocytes and the sensitivity to augmentation of null cells in cancer patients with different stages of diseases. Methodologies involving cell isolation and mixture techniques, use of monoclonal and polyclonal reagents, receptor-ligand binding studies, and analyses of protein and mRNA synthesis are proposed.